Cytochrome P450 (CYP450) enzymes are responsible for breakdown of most of the current drugs on the market. Consequently, each new molecular entity or drug candidate must endure rigorous toxicity testing in preclinical trials that includes testing for potential drug-drug interactions as a result of CYP450 inhibition or activation. As a result, there has been increasing demand for easy to use and more efficacious compositions, methods, kits and assays that are amenable to high throughput screening to monitor CYP450 enzyme inhibition and activation.